1. Field of the Invention
The present invention relates to a vibrator that operates in a vibration mode of in-plane vibrating in a vibrating surface, and a vibrating gyroscope that detects an angular velocity applied to a vibrator around a rotation axis perpendicular to a vibrating surface.
2. Description of the Related Art
A vibrating gyroscope detecting an angular velocity includes a vibrator having a first vibration mode (drive vibration mode) of vibrating along a drive axis perpendicular to a rotation axis and a second vibration mode (detection vibration mode) of vibrating along a detection axis perpendicular to the rotation axis and the drive axis. When the vibrator vibrating in the drive vibration mode rotates around the rotation axis, a Coriolis force along the detection axis is applied to the vibrator. When the Coriolis force is applied, the vibrator vibrates in the detection vibration mode. The vibration amplitude of the detection vibration mode becomes an amplitude that corresponds to the magnitude of the angular velocity of a rotational movement, in other words, the magnitude of the Coriolis force occurring due to the angular velocity of the rotational movement. Therefore, by detecting the vibration amplitude of the detection vibration mode, it is possible to detect the angular velocity of the rotational movement.
The structure of a vibrator used for a vibrating gyroscope varies (refer to, for example, Japanese Unexamined Patent Application Publication No. 6-42971 and Japanese Unexamined Patent Application Publication No. 2000-249554). A type of vibrator is configured in an annular shape within a surface perpendicular to a rotation axis (in particular, refer to Japanese Unexamined Patent Application Publication No. 6-42971).
FIG. 1A is the plan view (X-Y plane plan view) of a vibrating gyroscope 101 including an annular vibrator of the related art. The vibrating gyroscope 101 has a rectangular plate shape, in which an aperture is provided, and includes a frame portion 102, a support beam 103, a coupling beam 104, and a vibrator 105. The frame portion 102 is a part having a rectangular frame shape and configuring the outer periphery portion of the vibrating gyroscope 101. The support beam 103 is provided in the central portion of each of four sides of the frame portion 102, and parallel to each side of the frame portion 102, and both end portions thereof in a longitudinal direction are joined to the frame portion 102. The coupling beam 104 is orthogonally joined to the center of each support beam 103. The vibrator 105 is a part having an annular shape, and the four points thereof are supported by the coupling beams 104.
FIG. 1B is a pattern diagram explaining deformation in the drive vibration mode of the vibrator 105. The vibrator 105 is driven so as to expand and contract in phases opposite to each other along each of an X-axis and a Y-axis. FIG. 1C is a pattern diagram explaining deformation in the detection vibration mode of the vibrator 105, the detection vibration mode corresponding to a state where a Coriolis force is applied to the vibrator 105. In the vibrator 105, a vibration due to driving and a vibration due to the Coriolis force occur in directions perpendicular to each other. Therefore, when the Coriolis force is applied, the vibrator 105 expands and contracts in a direction inclined from the X-axis and the Y-axis. Accordingly, in the vibrator 105, in response to the magnitude of the Coriolis force applied to the vibrator 105, the position of a node point (the node of a vibration) or an antinode point (the antinode of a vibration) turns out to change (rotate).
In this way, the position of the node point or the antinode point in the vibrator 105 changes in response to the magnitude of the Coriolis force applied to the vibrator 105, and in the vibrator 105, no point exists that continuously becomes the node point. Therefore, it is necessary for the vibrator 105 to be supported by the support beam 103 or the coupling beam 104 so that the displacement of each point is not disturbed.
In addition, usually, it is desirable that a detection sensitivity for an angular velocity is high in a vibrating gyroscope. The detection sensitivity for an angular velocity is expressed as a value proportional to the product of the maximum value of the Coriolis force applied to the vibrator and a detected voltage (hereinafter, referred to as a detection efficiency) output per 1 N (Newton) of the Coriolis force. The maximum value of the Coriolis force is expressed as the product of the mass of the vibrator, the maximum velocity of the displacement of the vibrator in the drive vibration mode, and an angular velocity applied to the vibrator. Accordingly, the detection sensitivity for the angular velocity is expressed as a value proportional to the product of the detection efficiency, the mass of the vibrator, and the maximum velocity of the displacement of the vibrator in the drive vibration mode.
The detection efficiency, the mass of the vibrator, the maximum velocity of the displacement of the vibrator in the drive vibration mode, and so forth have correlations not only with the detection sensitivity but also with the thickness of the vibrator, a width dimension, a stiffness property, a resonant mode, and the resonant frequency thereof.
In recent years, the miniaturization of a vibrating gyroscope has been strongly desired. In general, when a vibrator becomes small, the resonant frequency of the vibrator becomes high. Therefore, when a vibrating gyroscope including a small vibrator has been installed in a digital camera or the like, a difference between the resonant frequency of the vibrator and the frequency of a hand movement becomes large. Therefore, a sensitivity for the hand movement or the like becomes low in some cases.
Therefore, the vibrator is caused to have a specific structure or the vibrator is caused to vibrate in a specific vibration mode, and hence, even if the vibrator is small, it is possible to prevent the resonant frequency of the vibrator from being increased.
Furthermore, so as to improve the drift characteristic of the vibrating gyroscope, it is necessary for both of the drive vibration mode and the detection vibration mode to share a common node point.
By supporting the vibrator using the common node point, it is possible to prevent a vibration from leaking from a supporting portion supporting the vibrator or prevent a undesired vibration from propagating from outside, and it is possible to obtain a good drift characteristic.
The resonant frequency of a vibrator is defined by a vibration mode depending on the shape of the vibrator, a stiffness property, and a mass, and, in the vibration mode, the stiffness property or the mass is changed by adjusting the thickness and width dimensions of the vibrator, and hence, it is possible to change the resonant frequency. However, when the resonant frequency has been changed by adjusting the thickness and width dimensions of the vibrator, a characteristic other than the resonant frequency has also been changed, and it is difficult to improve a detection sensitivity for an angular velocity, in some cases.
In addition, in the same way as the vibrating gyroscope 101 including an annular vibrator of the related art, in the configuration where the position of the node point or the antinode point changes in response to the magnitude of the Coriolis force applied to the vibrator, no point exists that continuously becomes the node point in the vibrator. Accordingly, the vibrator turns out to be supported in a vibrating point, and the leakage of a vibration from the supporting portion supporting the vibrator or the propagation of a undesired vibration from outside occurs. In addition, the vibration of the vibrator is disturbed, the resonant frequency changes, and the detection sensitivity for the angular velocity becomes low in some cases.